Metallurgy of chains

ABSTRACT

Driven chains formed from ferrous metal are subjected to isothermal transformation resulting in bainitic microstructure.

United States Patent [1 1 Fashfellow et al.

[ Dec. 31, 1974 METALLURGY OF CHAINS [75] Inventors: George H. Fashfellow, St. Charles;

Dort Fauntleroy, Geneva; Arnold A. Goetze, St. Charles, all of Ill.

[73] Assignee: Moline Corporation, St. Charles, 111.

[22] Filed: Sept. 13, 1973 [2]] App]. No.: 397,119

[52] US. CL- 74/245 R, 74/245 C [51] Int. Cl. F16g 13/02 [58] Field of Search 74/245 R, 245 C [56] I References Cited UNITED STATES PATENTS 12/1962 Onulak 74/250 R X 3,302,388 2/ 1967 Gentsch 74/245 R X Primary Examiner -Leonard H. Gerin Attorney, Agent, or Firm-Kinzer, Plyer, Dorn & McEachran [57 ABSTRACT Driven chains formed from ferrous metal are subjected to isothermal transformation resulting in bainitic microstructure.

4 Claims, 4 Drawing Figures METALLURGY OF CHAINS This invention relates to sprocket-driven chains of the kind used on conveyors and for transmitting power.

Malleable cast iron is a conventional material for the chains of the kind involved; also medium carbon steel of carbon content in the range of about 0.3 to 0.6.

In July, 1971 the Malleable Founders Society (Cleveland, Ohio, U.S.A.) published the following data concerned with the latest evaluations of mechanical prop- 10 erties of malleable castiron:

TABLE 1 FERRlTlC MALLEABLE IRON: (ASTM A 47-68) Tensile Strength Yield Strength Elongation min. min. min. min. Grade p.s.i. kgJmm' p.s.i. kg./mm min. in 2" 32510 50,000 35.0 32,500 23.0 l 350l8 53,000 37.5 35,000 24.5 l8

TABLE 2 PEARLlTlC MALLEABLE IRON: (ASTM A 220-68) Tensile Strength Yield Strength" Elongation min. min. min. min. Grade p.s.i. kgJmm p.s.i. kgJmm min. in 2" higher tensile and higher yield strengths may be ob-- tained from any of the grades of material in the table by use of a conventional quench-and-temper treatment.

Higher tensile and higher yield strength are indeed required for the type of chain we manufacture, requiring that quench-and-temper treatment be applied particularly to malleable iron grades 70003, 80002 and 90001 to establish tensile strength in excess of 80,000 p.s.i. while restoring some ductility by the temper treatment. In spite of this, experience. inthe field reveals unexplained failure of highly stressed chains (e.g., chain used to convey logs) particularly when subjected to power surges, shock due to sprocket jams and so on.

It can be appreciated that a chain failure when conveying logs of the size handled on terrain slopes in the Pacific Northwest can be a catastrophy of fatal magnitude to say nothing of what a cascade of timber weighing tons can do to the equipment. The same analogy prevails within industrial plants where power chains are traveling at considerable speed.

The enhanced mechanical properties achieved by quench-temper should withstand these stresses, even though of extraordinary magnitude.

There are, however, failures not. necessarily assignable to poor mechanical properties. Thus, on the basis of field studies we have been able to detect failures doubtless caused by gradual fatigue which started at a crack or fissure in the casting, a defect not necessarily associated with poor elongation or ductility. Our foundry controls are of exceptional reliance (X-ray inthe users of chain-driven equipment to operate that equipment with more assurance of sustained operation under high stresses. Specifically the object of the present invention is to construct parts of a sprocket-driven chain from malleable cast iron or medium carbon steel in which the microstructure is essentially bainite.

In the drawing:

.FIGS. 1 and 2 are curves showing quench andtemper properties of certain ferrous materials; and

FIGS. 3 and 4 are perspective views of chains to which the present invention may be applied.

Malleable cast iron has an accepted definition, (ASTM, 'A60270; SAE, Jl58 for the ferrite grade): The microstructure shall consist of temper carbon nodules distributed in a matrix of ferrite [typified by grade M3210] and the Microstructure of other grades shall consist of temper carbon nodules distributed in a matrix of ferrite and tempered pearlite in case of airquenched castings [typified by grades M4504 and M5003] .and tempered martensite in case of liquidquenched castings [typified by grades M5503, M7002 and M8501].

Succinctly, in malleable cast iron the carbon (or graphite) is predominantly free in nodular form and very little if any is combined. See US. Pat. No. 3,463,675.

The present invention involves chain structure made from malleable cast iron or medium carbon steel, each form of ferrous metal being transformed to bainite. Thus, chains of the kind involved have been made conventionally from malleable cast iron (cast parts) or fabricated from medium carbon steel forgings. We start with either of these conventional ferrous materials but treated to obtain the bainite transformation microstructure for reasons now to be explained.

FIG. 1 presents curves showing'mechanical properties of 1050 steel developed by quench-and-temper; quench in oil and reheat to temper at the temperatures shown. This steel is acceptable for the chains we manufacture. Ordinarily the part to be quenched is at a temperature well in excess of l,400F and is subjected instantly to a quench, at say 200F, whereupon the temper treatment is applied. But thermal stressing is involved,-represented by the shaded area.

FIG. 2 presents similar curves'applicable to quenchand-ternper applied to malleable cast iron; again the potential thermal stressing area is shaded.

Thermal stressing as thus imposed by quench-temper in an effort to improve mechanical properties would be responsible for inducing microscopic fissures (not ordinarily detectable by X-ray inspection) amounting to a precursor of the larger cracks we have observed in driven chains, specifically in those chains having parts with sharp corners or having drastic changes in thickness (e.g., undercuts) between adjacent sections.

Accordingly, under the present invention, we depart from the conventional teaching for obtaining enhanced mechanical properties in a malleable cast iron or a medium carbon steel powered chain, and instead employ for the chain ferrous parts in which the microstructure is essentially bainite.

Bainite microstructure is well known and is named for one of the inventors: see for example Bain US. Pat. No. 1,924,099. The value of the structure has been repeatedly recognized: US. Pat. Nos. 2,885,284; 3,338,709;'and 3,414,442. Bainitic microstructure is developed by first heating the ferrous part to a temperature and for a time sufficient where austenite is uniformly developed (the carbon dissolves in gamma iron) whereafter the part is quenched at a lower temperature and held at that temperature until the austenite transforms isothermally (constant temperature) to the bainite microstructure, and then is allowed to air cool.

In the present context what is critical is that isothermal transformation to bainite, in malleable cast iron or medium carbon steel, takes place at a temperature above about 475F and consequently the conventional quench-and-temper treatment presently prevailing, where the quench takes place at about 200F, is avoided, thereby reducing the possibility of thermally induced micro fissures. At the same time, bainite pres-- formation to bainite:

TABLE 3 BHN: 321 I Tensile: l62,735 p.s.i. (load SL050 pounds) Elong.:' 3%; Yield: [28,819 p.s.i.

Either of the ferrous materials, malleable cast iron or medium carbon steels, may be alloyed for specific purposes in'no way interfering with attainment of bainitic microstructure.

While we have extended our disclosure to explain metallurgical phenomenon involved, it should be emphasized again that the standard approach to field failures of sprocket-driven chains has been to rely upon the quench-and-temper approach to achieve higher values of strength and ductility, or even to steer in a whollyvdifferent direction as under the disclosure in U.S. Pat. No. 3,071,98l where fissures and cracks in a chain element are sought to be avoided by retaining an austenitic microstructure on the surface of the part in which is dissolved an additional non-ferrous metal while developing a martensitic sub-structure with the additive metal diffused between austenite and martensite.

FIGS. 3 and 4 are perspectives of typical chains to which the present invention may be applied. The chain in FIG. 3 comprises links as 10 having side bars 1 1 and barrels 12, the latter having apertures 13 for accepting pins 14 which articulate the links. The links have slats 15 in a plane normal to the plane of the related side bars. Bainitic microstructure under the present invention is induced in all parts, except possibly pins, cotters and washers if used, to avoid stress failure at corners as 18 or failure where there is a change in section thickness as at 20.

The invention may be applied as well to the chain links of simplified configuration shown in FIG. 4 because of the possibility of failure at the corner configuration 22, where the side bars 23 are joined to the end bars 24.

The chain links shown in FIGS. 3 and 4 are given by way of illustration; the invention, for example, may be applied to chains composed of detachable links in which an end bar at one end of one link is clasped by a hook end on the adjacent link. We have given mechanical properties for austempered malleable iron suitable for chains. Values for 4140 steel, austempered at 700F to form bainite are: R 42-46, Tensile 212,000 p.s.i. Other medium carbon steel chain parts may also be transformed isothermally to bainitic microstructure.

We claim:

1. A sprocket-driven chain having links each comprising a side bar part and an end part by which one link is articulated to another, each link in the chain being formed from a ferrous material selected from the group consisting of malleable cast iron and medium carbon steel in which the microstructure is essentially bainite.

- 2. A chain according to claim 1 in which the side bar for each link includes a slat in a plane normal to the plane of the side bar, the side bar and its slat having the microstructure of claim 1.

3. A chain according to claim 1 in which the bainite transformed isothermally at a temperature above 475F.

4. A chain according to claim 2 in which the bainite transformed isothermally at a temperature above 475F. 

1. A SPROCKET-DRIVEN CHAIN HAVING LINKS EACH COMPRISING A SIDE BAR PART AND AN END PART BY WHICH ONE LINK IS ARTICULATED TO ANOTHER, EACH LINK IN THE CHAIN BEING FORMED FROM A FERROUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF MALLEABLE CAST IRON AND MEDIUM CARBON STEEL IN WHICH THE MICROSTRUCTURE IS ESSENTIALLY BAINITE.
 2. A chain according to claim 1 in which the side bar for each link includes a slat in a plane normal to the plane of the side bar, the side bar and its slat having the microstructure of claim
 3. A chain according to claim 1 in which the bainite transformed isothermally at a temperature above 475*F.
 4. A chain according to claim 2 in which the bainite transformed isothermally at a temperature above 475*F. 